The present invention relates to ice-breaking means and, more particularly, ice-breaking means adapted for use on ships which act mainly in icy sea area, e.g., oil-rig vessels for polar oil fields and amphibian supply boats for cargo transportation.
Conventionally, oil-rig vessels and supply boats for use in icy sea areas have been constructed as ice breakers or designed to have ice-breaking function.
In these conventional ice-breaking ships, the wedging and ice-breaking are performed by means of the kinetic energy possessed by the ship herself and, therefore, the ship herself must be fully equipped for ice breaking. To this end, it has been necessary to make the ship's size considerably large, or to provide the ship with a large propulsion power to obtain a speed high enough to cause an effective ice-breaking force when colliding and impinging upon the mass of ice.
However, these conventional measures are quite incompatible with the requisites for oil-rig vessels under operation. Namely, oil-rig vessels have to keep the position for continuing the operation and, therefore, do not move so largely. Thus, ice-breaking relying upon the kinetic energy of the ship cannot be effectively used for oil-rig vessels, especially when it is under operation.
Also, it is not a good policy to make the ship's hull large, especially in case of supply boats intended for relatively small scale of cargo transportation, because the enlarged size inevitably leads to an uneconomically high cost and other inconveniences.
It is therefore an object of the invention to provide ice-breaking means suitable for use for oil-rig vessels, which can afford the ice breaking without the movement of the ship's hull itself.
It is another object of the invention to provide ice-breaking means for ships capable of performing multiple functions of breaking ice, propulsion of the ship and turning of the ship.
It is still another object of the invention to provide ice-breaking means which do not necessitate to make the ship large and, accordingly, suitable for use on ships such as supply boats intended for transportation of small scale.